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Alkali-activated fly ash foams – mechanical, chemical and physical properties
Alkali-activation of fly ash together with an aluminum powder blowing agent led to the synthesis of inorganic fly ash-based foam. The aluminium powder reacts with the alkalies from the activation solution. Hydrogen is released during this reaction and creates a closed-pore structure. The amount of liquid activation solution and aluminium powder was optimized considering proper pore distribution and feasible bulk density of the resulting foam. The viscosity of the initial mix was found as a crucial factor for the foaming process as well as for the stability of the fresh foam.
The fly ash foam is characterized in terms of its compressive and flexural strength, thermal conductivity and capacity, resistance to chemically aggressive environments, fire resistance and 2D morphology. The fire resistance test shows, that almost all mass loss occurres below 500°C and the biggest volume change take place between 800°C and 1100°C. An excellent chemical durability stems mainly from the closed-pore network and absence of leachable Ca in the system. Experiments and micromechanical simulations prove that reasonable bulk densities lie in the range of 400 to 800 kg/m3.
The joint research project AERIUS (BMBF), is working to determine the effectiveness and efficiency of CAF in comparison to pure water, water with foaming agents and nozzle-aspirated foams in an extensive series of firefighting experiments. The poster deals with a series of extinguishing tests with mixed-material burning cribs.
This work investigates the fire phenomena of rigid polyurethane foams (RPUF) in detail. To elucidate structure-property relationships systematically varied sets of foams were prepared. RPUF were synthesized with different densities using water and pentane as blowing agent. What is more, a flame retarded RPUF and rigid polyisocyanurate-polyurethane foams were examined. The comprehensive understanding of the processes taking place during combustion is the foundation of customized development of successful flame retardant approaches.
Advanced cone calorimeter investigations provide insight into the fire behavior under forced flaming conditions. Thermocouples in the inside of specimens give information about the temperature gradient and temperature of the pyrolysis zone during combustion. Furthermore, fire phenomena were characterized using SEM, LOI and thermal analysis. By using a multi-methodological approach and systematically varied sets of foam materials, new insights into the burning of RPUF were won. The detailed knowledge of fire phenomena is essential for future development of tailored flame retardant strategies for RPUF.
Rigid polyurethane foams (RPUF) are widely used in industry and daily life because of their outstanding mechanical and thermal insulating properties. While their convenient mechanical characteristics predestine these materials for shock absorption, their low thermal conductivity is responsible for their excellent thermal insulation properties. A principal characteristic affecting not only the use properties, but also the burning behaviour, is the density of RPUF.
In case of fire, cellular polymers like RPUF behave differently from bulk materials. The reason for their comparatively high ignitability is the high rate of temperature rise on the surface when exposed to heat, which is due to their cellular structure and characterised as low thermal inertia. The heat build-up on the surface results in a short time to ignition. Therefore foams are able to develop fire and large amounts of smoke within a short period of time. Even though their fire load is quite low because of their low density, their heat release rate is high. These burning properties are not only a consequence of the chemical consistence of such materials, but also a result of their morphology.
The aim of the work is to investigate the fire phenomena of RPUF. Characterised by simultaneous physical and chemical processes which interact, depend, and compete with each other, the combustion of RPUF is a highly complex occurrence. Therefore it is necessary to study all aspects in detail. The fire phenomena that were examined are gasification, liquefaction, charring and structural integrity as well as collapse. The melting of cellular polymers and dripping of pyrolysis products, together with the ability to form pool fires, are the main hazards in fires involving foams. Structural collapse via melting or decomposition, or the retention of the foam’s morphology through charring, are the main characteristics of their burning behaviour. Cellular structure is a further important factor influencing the materials’ response to fire, and deserves examination in greater depth. Since the cells in closed-cell foam are filled with the blowing agent used to produce the material, and this blowing agent can be inert (carbon dioxide) or highly flammable (pentane), this component also affects the burning properties and will be investigated. Examination of the influence of the macroscopic morphology, namely the cell size and thickness of cell walls, will contribute to the study.
In order to provide comprehensive insight into the processes taking place during combustion, and to elucidate structure-property relationships, a set of foams with systematically varied properties was prepared. RPUF was obtained using water and pentane as a blowing agent. Besides RPUF, a flame-retarded RPUF and rigid polyisocyanurate-polyurethane foam were examined, since these foams are known for their higher stability from a thermodanymic point of view. As a flame retardant active in the gas phase, triethylphosphate was used.
Using a multi-methodological approach, the complex interaction of fire phenomena was studied in detail. Cone calorimeter measurements provide insight into fire behaviour under forced-flaming conditions. They were carried out in an horizontal and a vertical orientation to account for the effects of melt flow and dripping. Sample-holders were equipped with glass windows to monitor the materials’ response to forced-flaming conditions with a video camera. Thermocouples were inserted into the specimens, giving information about the temperature gradient in the inside of the sample and the temperature of the pyrolysis zone during combustion. Changes in the morphology and thickness of the pyrolysis zone were examined using a hot-stage microscope, as well as SEM images of cross-sections of quenched foam specimens. The determination of the Oxygen Index and the use of thermogravimetry measurements rounded out the investigation.